[Haskell-beginners] Strange "Not in scope" error message

[Matthew Moppett]

I have a file with the following relevant lines:

import qualified Control.Concurrent as C

...

isCancelled = C.isEmptyMvar . stopConcurrentProcess

Trying to compile this or run it in ghci yields a puzzling error message:

Not in scope: `C.isEmptyMvar'
    Perhaps you meant one of these:
      `C.isEmptyMVar' (imported from Control.Concurrent),
      `C.isEmptyChan' (imported from Control.Concurrent)

Any idea what could be going wrong?
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